1. Field of the Invention
This invention relates to an improvement in an electrochromic display device (ECD) utilizing an electrochromism phenomenon, and particularly concerns an ECD wherein area of the effective electrodes varies in a manner similar to that of a seven segment numeral indicator.
2 Description of the Prior Art
An ECD is a display device which utilizes a specified solution (substance) which exhibits an electrochromism phenomenon (for short EC-solution), whereby the EC-substance electrochemically forms a color indication product on a surface of one of a pair of electrodes, disposed with the EC-substance inbetween, when a voltage is applied to the electrode pair.
A general ECD structure is schematically shown in FIG. 1, wherein a container 1 contains an EC-solution solution 2 and an electrode pair consisting of an indication electrode 3 and a counter-electrode 4. A color indication product is deposited on the indication electrode 3 when a charge is supplied from a battery 5 through a switching means 6. B6 changing-over switch 6, the polarity of the current is reversed, and therefore the supplied charge is removed from the indication electrode 3.
Generally, an ECD can be divided into two broad categories: organic type; and inorganic type. An ECD of the organic type utilizes a biologen derivative for a coloring surface, and an ECD of the inorganic type utilizes a tungsten oxide for a coloring substance. Both types of ECD are in general well known.
Since an ECD utilizes an electrochemical electrochromism phenomenon on the electrode pair with an high conductivity EC-solution interposed inbetween, the supplied charge density at the indication electrode changes depending on the area thereof. Therefore, the color display density at the indication electrode is changed corresponding to change of the total area of the effective indication electrode when the area of the counter-electrode is constant. Accordingly, where an ECD is used for selective indications of numerals 0 to 9, that is, as a figure display device of seven segments type, the color density of the display at the face of the indicating electrode changes for different numerals, since total area of the effective electrode is different for every numeral or mark. This is a primary cause of irregularity of display color density between the numerals.